Referring to FIG. 1, the present invention relates to the incorporation of information at the molecular level. The inspiration for sequential information storage is DNA, which uses hydrogen bonding to encode the information. A hydrogen bond donor or acceptor is a heteroatom (usually N or O) which may use either its lone pair of electrons (acceptor, negatively polarized) or attached hydrogen atom (donor, positively polarized) to reversibly interact via electrostatics with an opposing donor or acceptor in a non-covalent manner. The nucleobases are actually a “code” within a code, and display coplanar arrays of 2-3 hydrogen bond donor/acceptors (A's or D's in slide) depending on their identity as A, T, C, or G. Thus, only those nucleobases which have complementary sets of A/D's will recognize each other and this forms part of the basis for double helix formation in a sequence-specific manner. Each strand of DNA contains a particular sequence of nucleobases connected by a sugar-phosphodiester backbone which pairs up with a strand containing the complementary sequence.
FIGS. 2 and 3 (the same but some nitrogen (N) and oxygen (O) atoms have been highlighted in FIG. 3) give examples of coplanar arrays which are designed based on the example of DNA. This typical coplanar and linear 1,3-disposition of D/A's is used in almost all present systems, the exceptions being Gong et al. as disclosed in J. Am. Chem. Soc. 2000, 122, 2635-2644, “A Highly Stable Six Hydrogen-Bonded Molecular Duplex”; which is based on more widely spaced amide groups. Strength of the association between interacting species is based on the number of primary and secondary hydrogen bonding interactions and is hence code dependent. Strong binding-generally requires at least two contiguous D's or A's and generally at least four (4) primary interactions. These systems often suffer from: conformational and tautomeric ambiguity; they are often relatively insoluble, requiring the addition of solubilizing groups on their periphery; the synthesis of higher than four (4) D/A pairs is often problematic and certain sequences have not ever been reported (e.g. DDDD/AAAA). In addition, the syntheses of these types of compounds are generally specific to the particular compound and each one generally requires a custom synthetic scheme.
Notwithstanding the above difficulties, these units have been used in the preparation of supramolecular polymers through their attachment as either telechelic end units onto short linkers or oligomeric/polymeric linkers and as side chains through addition as functionalized comonomers in copolymerization schemes. Such schemes which have been described in the prior patent literature are discussed below.
U.S. Pat. No. 6,320,018 describes the synthesis of a supramolecular subunit based on a ureidopyrimidine heterocycle which is self-complementary through a linear and coplanar AADD arrangement of hydrogen bond donors/acceptors (D's/A's) or its tautomeric form (ADAD). These subunits are appended as end groups onto short (though one siloxane example is oligomeric with MW=6000 g mol−1) monomer backbones. The self-association of the end groups in the solid state through strong, selective and reversible hydrogen bonding mimics the strength of a weak covalent bond and “polymerizes” the monomers through this association such that they take on the properties of a much higher molecular weight material similar to that of a true polymer material. The approach is based on a single heterocyclic subunit which does not provide the option of altering either the kinetics or thermodynamics of the non-covalent hydrogen-bonding interactions between associating end groups.
U.S. Pat. No. 6,803,447 describes the synthesis of copolymers which incorporate both well known monomers and monomers that have been functionalized with self-associating subunits described above. The incorporation of the self-associating subunits provides reversible crosslinking in the material to generate a material which behaves as if it were crosslinked under ambient temperature. The virtual crosslinking behaviour can be reduced at elevated temperature and thus increases the ease of processing of the material in comparison to a regularly crosslinked polymer.
U.S. Pat. No. 7,025,813 describes the synthesis and formulation of inks which incorporate either self-associating end groups (one or two) or end groups which are complementary to other additives which must be present for the association event to occur. This provides the inks with either solvent or phase change behaviour such that evaporation of the solvent leads to solidification of the dye or a change in temperature changes the dye's phase from liquid to solid (or vice versa).
Present technologies use only a single type of hydrogen bond donor/acceptor unit as a crosslinking unit in these polymer composites. Tuning of the material properties in this case is achieved through variation of the amount of crosslinking agent incorporated in the material.
Therefore it would be very advantageous to provide a method of preparation of supramolecular polymers containing sequence-selective hydrogen bonding subunits in their-backbone which overcomes the aforementioned problems.